Re: [Boost-users] [preprocessor] extending loop limit >> 256

Subject: Re: [Boost-users] [preprocessor] extending loop limit >> 256
From: Paul Mensonides (pmenso57_at_[hidden])
Date: 2010-12-30 21:38:35

On Wed, 29 Dec 2010 13:01:22 +0100, Martin Pasdzierny wrote:

> using  BOOST_PP_LOCAL_ITERATE() and friends I found the maximum number
> of iterations to be limited to 256.
> 
> The according values seemed to be defined in
>     .../preprocessor/config/limits.hpp
> 
> But changing these values does *not* have any effect on the maximum
> number of iterations

No, it won't.  Those definitions are informational.

> Stepping through the libraries code I found the mechanisms far more
> complicated than expected.
> Now my question: is there any recommended procedure to increase the
> iteration limitation to values like 10000 ?
> 
> I found a couple of code locations explicitly repeating code with hard
> coded values from 1 ... 256.
> I guess at least this code needs to be extended, but probably consistent
> with some other changes.

Besides that, the main thing would be increasing how many digits are put 
together on the bounding limits.  I believe that the values in 
LOCAL_LIMITS are evaluated (to avoid repetitive use of TUPLE_ELEM) by the 
innards of the slot mechanism.  That mechanism does 10 digit (base 10) 
resolution.  The local iteration mechanism only pulls the last three 
digits (see boost/preprocessor/iteration/detail/{start,finish}.hpp at the 
ends).

I haven't specifically looked at what it would take with the file-
iteration mechanism, but it would be similar (but in more places).

-Paul